Problem: $ F = \left[\begin{array}{r}-1 \\ 2 \\ 0\end{array}\right]$ What are the dimensions of matrix $ F$ ?
Solution: The first dimension is the number of rows in the matrix. How many rows does $ F$ have? The second dimension is the number of columns in the matrix. How many columns does $ F$ have? So, $ F$ is a 3 $\times$ 1 matrix.